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Sep 24, 2013

Sun’s 11-Year Cycle Caused by Dark Matter, Say Physicists

The way the planets influence the flow of dark matter into the Sun could explain one of the biggest mysteries in science, say particle physicists

The Sun’s 11-year cycle is one of science’s greatest mysteries. Astronomers have watched in fascination for centuries as the number of sunspots increases and decreases over a regular cycle of almost exactly 11 years.

More recently, they’ve discovered that at the same time, the Sun’s visible light luminosity changes by about 10^-3 while its x-ray luminosity changes by a factor of hundred.

Nobody knows why this happens but various scientists have pointed to the remarkable correlation between the solar cycle and the orbital periods of the planets. In particular, Jupiter takes 11.8 years to orbit the Sun and there are a number of other tidal resonances of around 11 years associated with Saturn, Venus, Earth and Mercury.

The problem, of course, is that the tidal forces associated with the planets are tiny. Consequently, astronomers have concluded that they can have little or no effect on the Sun.

Today, Konstantin Zioutas at CERN near Geneva and a few pals suggest that something even more exotic could be the cause. Their idea is that the Sun is bathed in a constant stream of dark matter particles and that the gravitational fields of the planets focus this stream on the Sun as they pass through it during each orbit.

This kind of gravitational lensing is well known for light. Astronomers have found many examples of light from distant galaxies that has been focused towards Earth by closer ones.

But the focal length of such lenses on particles travelling at the speed of light is huge; far greater than the distance between any of the planets and the Sun.

So Zioutas and co suggest that the dark matter particles must be travelling much more slowly, perhaps at 1/100th or 1/1000th of the speed of light. They say that particle physicists have hypothesised a number of different particles with these kind of properties, such as axion-like particles and D-particles.

Zioutas and co go on to calculate that Jupiter could magnify such as stream by a factor of a million and that the extra energy it would send the Sun’s way would not be negligible. They say this could well account for the change in the Sun’s visible light and x-ray luminosities and of other less regular but unexplained phenomena.

That’s an interesting but highly speculative idea and these guys will be acutely aware of its shortcomings. For example, nobody has conclusively seen dark matter let alone understood how it might interact with the Sun to change its luminosity.

Even the idea that there is a preferred direction for the flow of dark matter is speculative. So the hypothesis that this stuff somehow explains the solar cycle is a significant leap.

Nevertheless, the correlation between the planetary tides and the solar cycle is hard to dismiss. Indeed, explaining this appears to be Zioutas and co’s major motivation. “There is nothing else one could imagine beyond the assumed flows of dark particles, which may settle such an oscillatory behaviour for the Sun being identical with the combined planetary orbital rhythm,” they say.

There seems little chance of settling the question one way or the other in the near future. However, the prospect of solving one of the greatest mysteries in science should provide astrophysicists and particle physicists with plenty of motivation to explore this idea further.